1. Field of the Invention
The present invention relates generally to cellular mobile communication systems and more specifically to a base station apparatus of the system.
2. Description of the Related Art
As illustrated in FIGS. 1 and 2, the base station apparatus of a conventional time-division multiple access (TDMA) cellular mobile communication system is comprised of a common control unit 1 which is connected to a mobile telephone switching office (MTSO), not shown, to provide overall control of the base station. Common control unit 1 is powered by a power supply unit 2 and mounted on an upper shelf 3 of the apparatus frame with the power supply unit 2. The base station serves two cells to which frequency ranges 1.5 GHz and 800 MHz, for example, are assigned respectively. To serve the 1.5-GHz range cell, a plurality of radio transceiver panels 4 are provided which are connected to the common control unit I and commonly powered by a power supply unit 5. Each transceiver panel 4 has a bandwidth of 0.25 MHz in the 1.5-GHz range and three time slots are multiplexed in the 0.25 MHz band of each transceiver. The transceiver panels 4 and power supply unit 5 are both mounted side by side on a middle shelf 6. The output terminal of each transceiver panel 4 is connected to a frequency division multiplexer 7A where it is multiplexed with the outputs of other transceivers and supplied to a diplexer 9A and transmitted from antenna 10A. Signals from mobile units located in the 1.5-GHz range cell are received by antenna 10A and fed through diplexer 9A to a frequency division demultiplexer 8A where they are decomposed into individual frequency signals and supplied respectively to transceiver panels 4. To serve the 800-MHz range cell zone, a plurality of radio transceivers 14 are provided which are connected to the control unit 1, powered by a power supply unit 15 and mounted side by side on a lower shelf 16. Each transceiver panel 14 has a bandwidth of 0.25 MHz in the 800-MHz range and three time slots are multiplexed in the 0.25 MHz band of each transceiver. The output terminal of each transceiver panel 14 is connected to a frequency division multiplexer 7B where it is multiplexed with the outputs of other transceivers 14 and supplied to a diplexer 9B and transmitted from antenna 10B. Signals from mobile units located in the 800-MHz range cell zone are received by antenna 108 and fed through diplexer 9B to a frequency demultiplexer 8B where they are decomposed into individual frequency signals and supplied respectively to transceiver panels 14. The control unit I receives an incoming call from the MTSO and, in response, selects one of the transceivers and one of the time slots assigned to it, depending on the destination address of the incoming call, and operates the selected transceiver for transmission to a mobile station. In return, a signal sent from the mobile station is received through demultiplexer 8A by the selected transceiver and applied through control unit 1 to the MTSO.
If any one of the power supply units 5 and 15 should fall, all transceivers powered by the failed power supply become inoperative and service breakdown occurs in the cell served by the failed transceivers.